Recent studies demonstrate that grip strength during everyday grasping activities is precisely regulated in an automatic manner to match the load of the grasped object and the frictional conditions present on the skin. Information from cutaneous tactile receptors is primarily responsible for this regulation. The objectives of this proposed applied research project are: 1) to elucidate the roles of cutaneous tactile receptors in controlling human grasp; 2) to determine if viable tactile responses can be obtained from cutaneous afferents in the quadriplegic hand; and 3) to determine if the responses of these natural sensors can be used to enhance the controlability of FNS neuromotor prostheses systems that restore grasp function in handicapped individuals who have paralyzed or asensory hands. The project utilizes percutaneous microneurography of the median nerve to directly study the responses of cutaneous afferents of the human hand. Initial studies will be performed with normal subjects while they grip an instrumented object attached to a servo controlled puller. The response specificity of identified tactile afferents will be studied for effects of stimulus rate, amplitude, direction of pull, and the interaction of simultaneous normal and shear forces applied to the skin. In addition to interaction of simultaneous normal and shear forces applied to the skin. In addition to single unit analyses, nerve records will be root mean square processed to determine if the massed activity from the recorded fascical can be used to estimate the average normal forces applied to the skin. The viability of the tactile afferents in the hands of C5 and C6 spinal injury patients will be studied using evoked potentials recorded from the median, ulnar and radial nerves to stimulation of the digital nerves. After establishing the patency of these patients major nerves, tactile afferents in the median nerve will be studied using microneurography while the skin of the fingers is mechanically stimulated. The final aspect of the project seeks to determine if the activity recorded using cuff electrode temporarily installed around the common digital nerve in a quadriplegic patient's hand can be used to estimate the magnitude of mechanical stimuli applied to the appropriate finger tip skin.